Segment Reporting - Operating Results and Total Assets Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Segment	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Number of Reportable Segments			3
Provision Expense Attributable To Business Segments And Reported	100.30%	125.00%	110.00%	111.60%
Net interest income (loss)	$ 157,370	$ 149,987	$ 467,793	$ 442,844
Provision (benefit) for loan and lease losses	9,500	8,500	27,750	24,500
Net interest income after provision for loan and lease losses	147,870	141,487	440,043	418,344
Non-interest income	50,909	46,257	148,333	146,786
Non-interest expense	124,642	122,281	371,844	371,420
Income before income tax expense	74,137	65,463	216,532	193,710
Income tax expense (benefit)	23,679	18,158	67,795	57,915
Net income	50,458	47,305	148,737	135,795
Total Assets	21,826,882		21,826,882		20,852,999
Segment Totals [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	161,968	155,112	474,143	450,053
Provision (benefit) for loan and lease losses	9,525	10,624	30,521	27,337
Net interest income after provision for loan and lease losses	152,443	144,488	443,622	422,716
Non-interest income	45,639	42,288	131,421	132,770
Non-interest expense	119,987	119,308	360,943	362,939
Income before income tax expense	78,095	67,468	214,100	192,547
Income tax expense (benefit)	24,898	18,792	67,034	57,567
Net income	53,197	48,676	147,066	134,980
Total Assets	14,705,218		14,705,218		13,857,335
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	61,249	56,430	175,058	161,008
Provision (benefit) for loan and lease losses	3,340	7,032	18,031	11,449
Net interest income after provision for loan and lease losses	57,909	49,398	157,027	149,559
Non-interest income	8,861	8,818	24,761	20,537
Non-interest expense	25,445	24,647	76,579	74,068
Income before income tax expense	41,325	33,569	105,209	96,028
Income tax expense (benefit)	13,148	9,347	32,940	28,710
Net income	28,177	24,222	72,269	67,318
Total Assets	6,251,726		6,251,726		5,682,129
Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	88,602	87,949	263,893	259,037
Provision (benefit) for loan and lease losses	6,159	3,570	12,156	15,816
Net interest income after provision for loan and lease losses	82,443	84,379	251,737	243,221
Non-interest income	27,307	25,387	77,571	87,654
Non-interest expense	79,735	82,748	241,314	251,759
Income before income tax expense	30,015	27,018	87,994	79,116
Income tax expense (benefit)	9,588	7,504	27,551	23,654
Net income	20,427	19,514	60,443	55,462
Total Assets	8,062,212		8,062,212		7,809,343
Other [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	12,117	10,733	35,192	30,008
Provision (benefit) for loan and lease losses	26	22	334	72
Net interest income after provision for loan and lease losses	12,091	10,711	34,858	29,936
Non-interest income	9,471	8,083	29,089	24,579
Non-interest expense	14,807	11,913	43,050	37,112
Income before income tax expense	6,755	6,881	20,897	17,403
Income tax expense (benefit)	2,162	1,941	6,543	5,203
Net income	4,593	4,940	14,354	12,200
Total Assets	391,280		391,280		365,863
Corporate and Reconciling [Member]
Segment Reporting Information [Line Items]
Net interest income (loss)	(4,598)	(5,125)	(6,350)	(7,209)
Provision (benefit) for loan and lease losses	(25)	(2,124)	(2,771)	(2,837)
Net interest income after provision for loan and lease losses	(4,573)	(3,001)	(3,579)	(4,372)
Non-interest income	5,270	3,969	16,912	14,016
Non-interest expense	4,655	2,973	10,901	8,481
Income before income tax expense	(3,958)	(2,005)	2,432	1,163
Income tax expense (benefit)	(1,219)	(634)	761	348
Net income	(2,739)	(1,371)	1,671	815
Total Assets	$ 7,121,664		$ 7,121,664		$ 6,995,664